Heretofore a variety of curable resin compositions are known in the coating industry including those comprising hydroxyl group containing acrylic or polyester polymers and a crosslinker such as melamine resins or organic polyisocyanates. The melamine resin-crosslinking compositions must suffer not only from volumetric shrinkage upon curing due to the emanation of lower alkanol by-products but also from a decreased weatherability particularly when exposed to acid rain due to the presence of triazine nuclei. The polyisocyanate-crosslinking system has problems of toxicity, decreasing weatherability with time and yellowing.
Japanese Laid Open (Kokai) Patent Application Nos. 36109/82 and 155660/83 disclose a system having an enhanced weatherability comprising room temperature-curable alkoxysilyl group-bearing acrylic polymers. This system has certain defects that the curing reaction proceeds slowly, that the cured product can be blotted with by-products produced by the hydrolysis of residual alkoxysilyl groups and that its rust prevention property is not satisfactory.
Japanese Patent Publication (Kokoku) No. 33152/88 discloses a thermosetting resin system utilizing a reaction between an alkoxysilyl component and a hydroxyl group-containing resin component. This system is also disadvantageous in that its curing reaction proceeds slowly and the resulting cured film exhibits a poor salt spray resistance.
It has long been known in the art to crosslink vinylpolysiloxanes with organohydrogenpolysiloxanes in the presence of a platinum catalyst. Unfortunately, the cured product of this composition is swellable with conventional organic solvents and thus exhibits poor solvent resistance as well as poor alkali resistance. This composition also has a poor overlaying property when used for coating purposes. These defects have precluded the composition from its application to coating compositions of general use.
In addition, the above hydrosilyl reaction by the organohydrogenpolysiloxanes has been utilized to obtain rubbery resilient products by reacting the organohydrogenpolysiloxanes with alkenyl group-bearing polymers and oligomers in the presence of a hydrosilylation catalyst such as chloroplatinic acid. See, Japanese Laid Open Patent Application Nos. 138230/89, 95266/82, 200807/82 and 277645/82.
All of the above compositions are reactive even at room temperature and, therefore, at least the catalyst must be kept separately from the remainder of the compositions immediately prior to use.
Japanese Laid Open Patent Application No. 294320/82 discloses a one-component curable resin composition comprising an alkenyl group-bearing polymer, a hydrosilyl group-bearing compound, a hydrosilylation catalyst and a stabilizing agent such as benzothiazole. However, it has been found that the stabilizing agent disclosed therein dose not fully satisfy with the stability requirements for practical application.
It has been reported in J. Japanese Chem. Soc., 5 , 541-546 (1990) that various acetylenic compounds are effective to regulate the hydrosilylation reaction.
We have found that the above problems may be solved by incorporating an alkynyl group-bearing polymer into a curing system containing an alkenyl group-bearing polymer, an organohydrogenepolysiloxane and a hydrosilylation catalyst. By incorporating the alkynyl group-bearing polymer, various properties of the resulting films may be greatly improved including weatherability, solvent resistance, alkali resistance, acid resistance, waterproofness, salt spray resistance, rust preventive property, anti-blotting property and so on. We have also found that when using the above composition for coating purposes, the use of organic solvents may be dispensed with. The present invention has its basis on these findings.
Accordingly, it is an object of this invention to provide a curable resin composition which is excellent in storage stability, weatherability, acid resistance, alkali resistance, waterproofness, salt spray resistance, solvent resistance, overlaying property and so on.
It is another object of this invention to provide a curable resin composition which is curable without volumetric shrinkage and thus may also be used for molding purposes.
It is a further object of this invention to provide a curable resin composition which may be used for coating purposes as solventless or high solids coating compositions.